The invention is thus concerned with measuring a torque at a defined location of a structural element in order either simply to obtain information about the torque occurring at said location and use this information for warning purposes, or to carry out controls using the information concerning the torque that occurs. It is known in principle to determine torque using suitable measuring elements, for example strain gages, which are applied at the sites where the torque occurs. In many cases, arranging a torque sensor at the measurement site entails considerable design disadvantages, meaning that less suitable design solutions are employed or that the measurement is carried out at another, less suitable location.
One example of this is the controlling of an artificial knee joint. Such artificial knee joints are provided with a high degree of damping in the stance phase in order to keep the joint stable in the stance phase. By contrast, when the knee joint is deliberately flexed, a low degree of damping must take effect. To control the damping, it is known to determine, in proximity to the knee joint, the torque occurring about the knee axis or near to the knee axis. However, since a knee extension moment of about the same order develops during bending of the knee joint, and also shortly before said bending of the knee joint, a clean divide between stance phase and swing phase is difficult to realize. The sensitivity of the control is adversely affected by this.
It is known that better differentiation between stance phase and swing phase is possible by determining a torque directly above the foot, in order to deliver a signal similar to the ankle moment. The arrangement of the sensor in the below-knee area, however, has the disadvantage that the below-knee tube of a modular below-knee prosthesis has to be specially designed, thus necessitating much more complex construction work. Moreover, prosthetic feet with an integrated tibia pylon cannot be used.